Media handling mechanisms in the field of thermal printing handle the print media, such as paper, by either shuttling the print media back and forth during the printing process or by rotating the media in one direction. When the goal is to efficiently move the print media so that minimal time is required to print multiple colors in color printing, the former approach is less desirable. A more effective approach is the rotation of the print media in one direction so that by the time the bottom of the page is printed, the top of the page is close to the print head for repetitive printing.
One approach which rotates the print medium in one direction uses a clamp that directly attaches the paper onto a circular rubber coated drum that also functions as a platen. Printing occurs directly on the drum and the paper or print medium motion is in a continuous circle. This method has the advantage of actuating the print medium clamp merely by reversing the direction of rotation of the drum. However, a disadvantage of this approach is that a wide and expensive print head is required because of the shallow tangent angle of the print head to the large diameter drum or platen.
Another approach utilizes two belts which rotate about three rollers, one of which is the printing platen. This approach permits the use of a relatively narrow print head with the attendant reduction in print head cost. However, a distinct disadvantage of this design is the difficulty in achieving good dot to dot registration from one printed pass to another in color printing because of the skew and lateral or x-direction instability of the twin belts.
These problems are solved in the design of the present invention by providing a paper handling assembly for use in a color printer wherein a final receiving substrate, such as paper or a transparency, can be precisely moved a number of times between a platen, a ribbon and a print head to achieve color printing.